[tor-bugs] #5298 [Core Tor/Tor]: Relay does not pick the right IP addr of local node when multiple interfaces are available (was: Relay does not pick the right IP addr of local node)

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#5298: Relay does not pick the right IP addr of local node when multiple
interfaces are available
-------------------------------------------+-------------------------------
 Reporter:  ciaccio                        |          Owner:  (none)
     Type:  defect                         |         Status:  new
 Priority:  Medium                         |      Milestone:  Tor:
                                           |  0.3.4.x-final
Component:  Core Tor/Tor                   |        Version:  Tor: 0.2.3.25
 Severity:  Normal                         |     Resolution:
 Keywords:  tor-relay, ipv6, reachability  |  Actual Points:
Parent ID:                                 |         Points:
 Reviewer:                                 |        Sponsor:
-------------------------------------------+-------------------------------
Changes (by teor):

 * keywords:  multihomed, ppp0, 3G, tor-relay, ip-detection => tor-relay,
     ipv6, reachability
 * status:  assigned => new
 * milestone:  Tor: unspecified => Tor: 0.3.4.x-final


Comment:

 I don't think this bug can happen in modern versions of Tor:
 * when Tor is configured with only a port, it binds to all local
 interfaces. It does not guess a local interface.
 * when Tor guesses an external IPv4 address to advertise, it guesses based
 on the external IP address discovered from a remote relay's response.

 That said, bugs like it still exist: it is possible for tor to guess an
 unreachable address.

 We might fix this as part of #24403, by trying to reach multiple addresses
 until one works. (We would also need to re-check reachability every hour,
 rather than just checking once.) Multiple reachability checks are
 important for IPv6 reachability, because there are likely to be more IPv6
 addresses available on local interfaces than IPv4 addresses.

--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/5298#comment:29>
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